The answer is the missing s3:ListBucket permission on the S3 bucket. Without this permission, the Lambda function cannot verify the bucket’s existence or check for existing object keys before writing, even though s3:PutObject is allowed. The AWS S3 API requires ListBucket for bucket-level operations like confirming the target bucket is accessible, and without it, write attempts fail with an AccessDenied error. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding that S3 write operations often implicitly depend on ListBucket, especially when the Lambda function uses the AWS SDK to write objects by key. A common trap is assuming PutObject alone is sufficient, but the SDK may perform a bucket listing first to validate the path. Remember the memory tip: “To write, you must first list—ListBucket is the key that unlocks the bucket.”
DEA-C01 Data Ingestion and Transformation Practice Question
This DEA-C01 practice question tests your understanding of data ingestion and transformation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Refer to the exhibit. A data engineer created this IAM policy for a Lambda function that reads from a Kinesis stream and writes to an S3 bucket. The Lambda function fails with an 'AccessDenied' error when trying to write to S3. What is the missing permission?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
s3:ListBucket on the bucket
Option C is correct because the Lambda function needs permission to list the bucket (s3:ListBucket) to verify the bucket exists and possibly to check for existing objects. The 's3:PutObject' action is allowed, but without 's3:ListBucket', the function may fail when trying to write if the key does not exist or for bucket-level operations. Option A is wrong because 's3:GetObject' is already present. Option B is wrong because 's3:DeleteObject' is not needed. Option D is wrong because 's3:PutObjectAcl' is not required.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
s3:ListBucket on the bucket
Why this is correct
ListBucket is often required for PutObject operations to verify bucket existence.
Related concept
Standard ACLs match source addresses.
✗
s3:GetObject on the bucket
Why it's wrong here
GetObject is already allowed on the bucket objects.
✗
s3:PutObjectAcl on the bucket
Why it's wrong here
PutObjectAcl is not needed for writing.
✗
s3:DeleteObject on the bucket
Why it's wrong here
DeleteObject is not required for writing.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DEA-C01 ACL questions on filtering logic and placement.
Data Ingestion and Transformation — This question tests Data Ingestion and Transformation — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: s3:ListBucket on the bucket — Option C is correct because the Lambda function needs permission to list the bucket (s3:ListBucket) to verify the bucket exists and possibly to check for existing objects. The 's3:PutObject' action is allowed, but without 's3:ListBucket', the function may fail when trying to write if the key does not exist or for bucket-level operations. Option A is wrong because 's3:GetObject' is already present. Option B is wrong because 's3:DeleteObject' is not needed. Option D is wrong because 's3:PutObjectAcl' is not required.
What should I do if I get this DEA-C01 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DEA-C01 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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